You can go out and buy a ninja costume, but what about making it yourself? If this idea scares you, perhaps because you have never made anything like this before or because you are just not that handy or artsy and crafty in general.
There are many costumes that you can make that do not even require sewing or any really difficult tasks, and so anyone can do it regardless of their skill.
Making Your Ninja Costume
For a basic ninja costume one all you will need is a pair of black pants, ten black shirts, and one black t-shirt.
Now comes the fun part, where you actually make the costume. First what you do is take one of the ten shirts and lay it out on a flat surface. Starting from the bottom of the shirt, you want to start folding horizontally upwards. Keep folding until you have something that looks at least somewhat like a think, large headboard.
Then grab the sleeves and pull them around your back, while placing the very middle of the shirt around your stomach. Tie the sleeves off around your back and then tuck all the remaining ends into the belt, so that as an end result it resembles a belt.
Then take another shirt and put it on normally, folding the sleeves back until it looks like a sleeveless shirt, then take the part of the sleeve that is inside out and make it into a sort of triangular shape, as best as you can. Let this part hang loosely over your shoulder, and the actual end of the sleeve should be up by your neck.
Then take the bottom part of the shirt and pull it over your head, so that it is on the back of your neck, but make sure that you keep your arms through the sleeves, so that you should end up having something that at least remotely resembles a vest around your arms.
The next step to making your ninja costume is to take yet another shirt and make a ninja hood out of it. Then you want to take another shirt and place it on your upper thigh, making sure that the collar is pointing towards your navel at an angle. Take a final shirt and do the same to your lower legs. Also do the same for your upper and lower arms, and voila, you are done.